1. Field of the Invention
The present invention relates to a display device, and more particularly, to a display device that adjusts a driving method according to luminance mode of the display device.
2. Description of the Prior Art
Display devices, an LCD for example, generate a color for a pixel through red, green, and blue sub-pixels. For example, when the red, green, and blue sub-pixels of the pixel have the same luminance weightings, the pixel displays gray levels of white and black. When the luminance weightings of the red, green, and blue sub-pixels are changed, different colors can be displayed. In general, the colors (red, green, and blue) of the sub-pixels are generated in several ways. For example, a backlight of the display device may generate white light, and the white light may be filtered by a color filter to generate the colors. Or, the backlight may have red, green, and blue light sources, so the color filter is not required, an RGB LED backlight being one example. When the LCD uses the color filter to generate the red, green, and blue colors, the low light transmittance of the color filter reduces the light penetrating the panel and increases the power consumption of the backlight. For increasing the light penetration of the backlight, a white pixel is added in the color filter. Thus, the light transmittance of the color filter is improved as well as the light penetration of the backlight, so that the power consumption of the display device can be reduced.
In general, for the display device with three sub-pixels (R, G, and B) or four sub-pixels (R, G, B, and W), the sub-pixels of the display device can be arranged in different ways. FIG. 1 is a diagram of an arrangement of the sub-pixels of a display device. A display panel A1 has red (R), green (G), and blue (B) sub-pixels. Each pixel P1 is defined by the red, green, and blue sub-pixels in a regular arrangement. For example, to display a white color on the pixel P1, each sub-pixel of the pixel P1 has the same luminance weighting, so the ratio of the luminance weightings is 1:1:1, such as each sub-pixel being 100% turned on. FIG. 2 shows another arrangement of the sub-pixels of a display device. A display panel A2 has red (R), green (G), blue (B) and white (W) sub-pixels. Each pixel P2 is defined by the red, green, blue and white sub-pixels in a regular arrangement. For example, to display a white color on the pixel P2, each sub-pixel of the pixel P2 has the same luminance weighting, so the ratio of the luminance weightings is 1:1:1:1, such as each sub-pixel being 100% turned on. FIG. 3 and FIG. 4 are other arrangements of RGBW sub-pixels differing from the regular arrangement in FIG. 2 according to the prior art. The sub-pixels in FIG. 3 and FIG. 4 are interlaced, and the sub-pixels of each pixel are driven with a specific ratio of luminance weightings, which is called pixel rendering technology. Please refer to FIG. 3. A display panel A3 utilizes 10 sub-pixels to define a pixel P3. Similarly, to display a white color in the pixel P3, when the red and green sub-pixels in the center are set to 100% luminance, the blue and white sub-pixels in the surroundings are set to 25% luminance respectively, so the ratio of the luminance weightings of the red, green, blue, and white sub-pixels of the pixel P3 is 1:1:0.25:0.25. From the comparison of FIG. 2 and FIG. 3, each sub-pixel in the display panel A3 has a larger area than the sub-pixel in the display panel A2. For example, the area of the pixel P2 corresponds to two sub-pixels of the pixel P3 (as shown by the dotted line in FIG. 3). The large sub-pixel of the display panel A3 improves the light penetration of the backlight but reduces the resolution. However, in the display panel A3, each sub-pixel of the pixel P3 not only belongs to the pixel P3, but also belongs to the pixels surrounding the pixel P3. Thus, the sub-pixel arrangement of the display panel A3 driven with the specific luminance weighting of the red, green, blue, and white sub-pixels can improve the light penetration of the backlight and the resolution of the display device. Please refer to FIG. 4 again. A display panel A4 utilizes nine sub-pixels to define a pixel P4. Similarly, to display a white color in the pixel P4, the ratio of the luminance weighting of the RGBW sub-pixels of the pixel P4 is 0.5:1:0.5:0.25. From the comparison of FIG. 2 and FIG. 4, each sub-pixel in the display panel A4 has a larger area than the sub-pixel in the display panel A2. For example, the area of the pixel P2 corresponds to one sub-pixel of the pixel P3 (as shown by the dotted line in FIG. 4). In the display panel A4, each sub-pixel of the pixel P4 not only belongs to the pixel P4, but also belongs to the pixels surrounding the pixel P4. Thus, the sub-pixel arrangement of the display panel A4 driven with the specific luminance weighting of the red, green, blue, and white sub-pixels can improve the light penetration of the backlight and the resolution of the display device.
In addition, the LCD can be categorized as a transmissive LCD, a reflective LCD, or a transflective LCD according to the backlight of the LCD. The transmissive LCD has a backlight for generating light beams that pass through the display panel. The reflective LCD has a reflective surface inside for reflecting ambient light. The reflective LCD collects the ambient light as it enters from the front of the display panel so that the reflective surface can reflect the ambient light through the display panel again. Thus, the reflective LCD can utilize the ambient light as all or part of light source. The transflective LCD has both transmissive and reflective modes. When the LCD is used in an outdoor environment or when the surroundings of the display panel are bright, the LCD can turn off or turn down the backlight inside, and utilize the ambient light reflected by the reflective surface as all or part of light source, i.e. the LCD displays the image with the reflective mode. When the LCD is used in an indoor environment or the surroundings of the display panel are dark, the LCD can turn on the backlight inside, i.e. the LCD displays the image with the transmissive mode. Thus, the power consumption of the LCD can be saved.
In conclusion, when the LCD is used generally in different kinds of portable electronic devices, the power consumption of the LCD plays an important role in design. As mentioned above, an LCD may be designed to have transflective control functions and a pixel array of red, green, blue, and white sub-pixels, so as to increase the penetration of the backlight and decrease the power consumption of the backlight. However, when the LCD operates in the reflective mode, the reflected light is absorbed twice by the color filter of the display panel so that the luminance of the reflected light in the red, green, and blue sub-pixels is even lower than in the white sub-pixel. Thus, the LCD may display incorrect gray levels or display different gray levels between different operating modes.